SOME SURFACE CHEMICAL ASPECTS OF GLASS-RESIN COMPOSITES. PART 1. WETTING BEHAVIOR OF EPOXY RESINS ON GLASS FILAMENTS
Technical rept. no. 1
NAVAL RESEARCH LAB WASHINGTON DC
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A study was made of the wetting behavior of epoxy resins on glass filaments and its relation to the fabrication and the properties of filament wound glass-resin composites. The experiments were designed to determine how wetting is affected by the surface finish on the glass, the molecular structure of the epoxy liquid, and the presence in the liquid of a curing agent. Wetting behavior on freshly drawn E-glass fibers was compared with the wetting of commercial HTS-finished E-glass filaments and of glass fibers coated with hydrolyzed silane finishing agents. It was found that the HTS and the silane finished glass were poorly wet by all the epoxy liquids regardless of the chemical structure of the liquid or the presence of amine. The dynamic advancing contact angle formed against a fiber as it moves into the liquid was generally about 10 to 20 degrees higher than the static, equilibrium advancing angle. The HTS and silane finished glass fibers were covered with a visible coating of the sizing material. The coating materials were only partially soluble in the epoxy liquids. Observations of filament winding on pilot plant equipment, as well as the examination of segments of impregnated glass roving taken from the machine, revealed that air bubbles amounting to a significant portion of the total volume were entrapped in the glass-resin composite. For optimum impregnation it is necessary that the resin wet the glass fiber at a zero contact angle and mechanical means must be provided in the winding operation of minimize air entrainment and to release air bubbles from the roving.